For most electronic equipment, and not least for electronic equipment employed in tele-communication systems, it is essential to provide an effective shield or screen with regard to electromagnetic radiation that may disturb and interfere with the operation of other electronic equipment. In order to prevent electromagnetic coupling (EMC) between electronic components it is therefore equally important to block out ambient electromagnetic radiation on the one hand and to shield against the emission of radiation on the other hand. Such a shielding may be provided for individual components as well as for PCB's carrying such components, board fronts and entire casings, such as magazines, enclosing such electronic equipment. The most common way of providing such a shield for all of the above mentioned applications is by way of a contact spring that with a base portion is fixed to a first surface of a component, a PCB, a board front or a casing and that contacts an opposite surface with contact spring tongues extending from the base. The same general type of contact spring is also frequently used for grounding purposes, whether for preventing harmful electrostatic discharge between electronic equipment or for earth-connecting an electronic component, that is creating a zero potential for said equipment or component.
In all of said applications it is vital for the contact spring to make good contact between the two surfaces and to securely maintain such contact even when a component or casing wall etc. is dismounted and reassembled one or several times. The attachment of the contact spring to the surface in question must also be secure so as to avoid that the contact spring itself falls off said surface and interferes with other components of the equipment.
However, none of the contact spring presented so far have been able to solve all of the above-discussed problems to a satisfactory degree. A common design for such contact springs is to provide a clamp portion through which the contact spring is attached to the relevant surface either by being pushed over one edge thereof or by being inserted into apertures formed in said surface. None of these suggestions provides a definite solution to the problems of maintaining a secure contact and of fixing the contact spring to the surface, since only one longitudinal side thereof is attached to the surface. The other side providing the spring action may be easily deformed so that contact is no longer guaranteed for all contact tongues or may even get caught in some object so that the entire spring is torn off from the surface. This may even happen before the component is finally mounted if a spring tongue gets caught for instance in the clothes of an installer. The forming of apertures for the clamp portions is a bad solution since even a small aperture in many cases deteriorates the shielding.
Specifically for the purpose of grounding adjacent board fronts in a magazine or other casing there is also the requirement that the attachment shall not interfere unacceptably with the standardized inner space of the normally U-shaped front. The reason for this latter requirement is the ever-increasing thickness of the employed PCB's, more and more commonly requiring the full available space of the board front. One approach to provide an attachment that does not interfere with said inner space is to attach one longitudinal side of the contact spring to the outer side surface of the board front by means of an adhesive. Although this solution requires no inner space it involves great efforts of cleaning the surfaces of both the board front and the contact spring before adhesion, and yet does not at all times prevent the contact spring from falling off during insertion of the respective board front.
A further approach to provide an appropriate contact spring for the above purposes is to employ an assembly consisting of a substantially flat elongated carrier plate that is attached to the respective surface by riveting and on which a contact spring is supported. Examples of such solutions are disclosed in U.S. Pat. Nos. 4,623,752 and 5,001,297. The two longitudinal edges of the contact spring are bent inwardly towards each other and extend below the carrier whereas the spring tongues span the carrier transversally. In this assembly the spring portion may be deformed completely until it engages the upper side of the carrier. Not only does this involve risks of permanent deformation of the spring by overloading, the full compression of the spring may also cause the spring to be disengaged from the carrier. In situations where an object such as a wall section is inserted incorrectly, such a design involves a great danger of the contact spring, or at least spring elements thereof, being completely cut-off by shearing action. The conventional attachment, such as by riveting, also takes up valuable space on the inner side of said surface and requires the use of tools.